Occurrence of dawn phenomenon without change in insulin clearance in patients with insulin-dependent diabetes mellitus.

To assess the possible role of increased insulin clearance in the pathogenesis of the dawn phenomenon, we compared plasma free-insulin concentrations, free-insulin clearance rates, and plasma glucose concentrations in eight subjects with insulin-dependent diabetes mellitus (IDDM) during infusion of insulin from midnight to 0800 h (0.15 mU . kg-1 . min-1) with a Biostator and a Harvard pump. During infusion of insulin with the Biostator, plasma free insulin decreased 40% (from 14 +/- 1 to 9 +/- 1 microU/ml, P less than .01), insulin clearance increased 54% (from 11 +/- 1 to 17 +/- 2 ml/min, P less than .05), and plasma glucose increased from 101 +/- 4 to 217 +/- 27 mg/dl, P less than .01. During infusion of insulin with the Harvard pump, neither plasma free insulin (14 +/- vs. 13 +/- 1 microU/ml) nor free-insulin clearance (12 +/- 2 vs. 13 +/- 2 ml/min) changed significantly, but plasma glucose increased from 100 +/- 3 to 167 +/- 21 mg/dl, P less than .01. The increases in plasma glucose during infusion of insulin with the Biostator and the Harvard pump were not significantly different (t = 1.44, P = .19). When insulin was delivered directly into test tubes with the Biostator and the Harvard pump, insulin concentrations in the test tubes decreased 46% over 8 h (P less than .05) with the Biostator, whereas no decrease was observed with the Harvard pump.(ABSTRACT TRUNCATED AT 250 WORDS)